SpaceTech developed a new high performance large aperture retro-reflector in cooperation with the GeoForschungsZentrum (GFZ) Potsdam and the University of Applied Sciences in Deggendorf. The new Single Element Hollow-Reflector (SEH-R) aims for navigation satellites in a GNSS orbit as e.g. Galileo, Glonass, GPS or Compass. This reflector offers superior performance against the currently used arrays consisting of many small reflectors. The main advantage of this concept is the capability to tune the far field characteristics, i.e. the maximized energy distribution, to the specific needs of tracking MEO satellites on orbits with different inclinations from ground stations located at different latitudes.

Comparison Far-Field Standard Reflector Array / SEH-R (Principle Image)Comparison Far-Field Standard Reflector Array / SEH-R (Principle Image)

The realization of a passive reflector places high challenges on
  • the overall concept,
  • optical quality and sensitivities
  • mechanical/thermal design,
  • materials
  • manufacturing and alignment tolerances
  • testing under 1g conditions.
Overall Design

A passive design with 3 reflectors of aspheric shape acting as aperture of about 20 cm diameter is selected. Extreme manufacturing and alignement accuracies as well as environment robustness are required providing challenges for design, analysis, production and product characterization.

The mechanical/thermal concept is based on Silicon Carbide (SiC) material for the reflector and support structure, a suitable mix of surface properties, temperature insulation, temperature trim areas and isostatic mounts towards the satellite. The utilization of SiC especially allows limiting the 1g distortions and performance verification under 1g conditions.

Alignment Technology

The misalignment of the three mirrors to each other shall be smaller than 0.2 acrsec. The following picture illustrates the theoretical far field (perfect alignment) and a tilted (misaligned by 0.2 arcsec) configuration.

Reflected Far Field (Left: Ideal; Right: 0.2" Tilt Errors)Reflected Far Field (Left: Ideal; Right: 0.2" Tilt Errors)

The University of Applied Sciences in Deggendorf supported the alignment concept and verification. The first alignment tests prove the feasibility of the concept. The picture illustrates the interferometrically measured alignment of two planar surfaces relative to each other, see pictures below for interferogram.

Alignment Test Sample InterferogramAlignment Test Sample Interferogram

 SEH-R Performance SummarySEH-R Performance Summary

*) Development cofunded by BMBF.